Adhesive for optical disks

ABSTRACT

The invention relates to an adhesive for optical disks exhibiting superior adhesive properties with resins such as polycarbonate or metals such as aluminum and gold, and possessing better wet heat resistance than conventional adhesives. The adhesive comprises (A) a urethane (meth)acrylate oligomer (B) a hydroxy (meth)acrylate in which the hydroxy group is 3 or more carbons spaced away from the (meth) acrylate, and (C) at least one photoinitiator.

FIELD OF THE INVENTION

The present invention relates to a photocurable adhesive for opticaldisks, and to optical disks made therewith.

BACKGROUND OF THE INVENTION

Recent progress of information technologies including computer devices,computer software, and communication technologies has allowed a highspeed conveyance of mass information. Along with this advancement,recording media which can record much more information at high densityhave been desired and the development of such recording media isongoing. An example of such high-density recording media is a DVD(digital video disk or digital versatile disk) which has been developedas a recording media for wide use in the next generation. The DVDdiffers from conventional CDs (compact disks) in that the DVD ismanufactured by laminating two disks. Therefore, an adhesive forlaminating these two disks is required. Hot-melt, heat-curable,anaerobic curable, and similar adhesives have been tried for laminatingdisks for DVD, but these adhesives have not been entirely successful.Hot-melt adhesives have insufficient heat stability and weatherability.Because the hot-melt adhesives soften at high temperature, the decreasedadhesive strength causes the laminated disks to separate and deform. Inaddition, since transparency of the adhesive is insufficient, it isdifficult to use hot-melt adhesives for the DVD with a two-layeredstructure comprising a translucent recording film. Heat-curableadhesives are unsatisfactory because heat curing causes the substratefor forming a disk to deform, and the curing time is long. Anaerobiccurable adhesives are also unsatisfactory because they require a certainperiod of time for curing, thereby resulting in reduced productivity.

Photocurable adhesives have been proposed to solve these problems. Forexample, UV curable adhesives comprising a urethane acrylate as a majorcomponent has been disclosed in Japanese Patent Applications Laid-openNo. 142545/1986 and No. 89462/1994.

However, UV curable adhesives known heretofore have also beenunsatisfactory. Conventional UV curable adhesives do not providesufficient adhesion to resins such as a polycarbonate for forming thedisks, aluminum for forming reflecting films, gold for formingtranslucent films, and the like, while producing cured products withsufficient moisture resistance.

SUMMARY OF THE INVENTION

An object of the present invention therefore is to provide a UV curableadhesive which exhibits superior adhesion to resins, such aspolycarbonate for forming the disks, aluminum for forming reflectingfilms, gold for forming translucent films, and the like. A relatedobject is to provide a UV curable adhesive that can produce curedproducts with excellent moisture resistance, in particular at relativelyhigh temperatures.

These and other objects and advantages of the invention will be readilyunderstood by those skilled in the art in view of the detaileddescription of the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As a result of extensive studies, the inventors of the present inventionhave discovered that the above problems can be solved by the followingadhesive for optical disks.

Specifically, in accordance with the present invention a photocurableadhesive for optical disks comprises the following components (A), (B),and (C):

(A) a urethane acrylate or methacrylate, referred to herein as(meth)acrylate comprising a backbone, urethane groups, and a(meth)acrylate group.

(B) a hydroxyalkyl (meth)acrylate, in which the hydroxyl group and the(meth)acrylate group are spaced apart by at least three (3) carbonatoms, and

(C) at least one photoinitiator. The adhesive composition of the presentinvention can also include at least one (meth)acrylate functionaldiluent (D) other than (B), and/or at least one non-(meth)acrylatefunctional diluent (E), as described more fully herein.

The urethane(meth)acrylate used as the component (A) is generallyobtained by reacting a polyol, a polyisocyanate, and a hydroxylgroup-containing (meth) acrylate.

The polyol that can be used to form the urethane (meth)acrylate can be adiol or a polyol. By way of illustration and not in limitation, thepolyol can be a polyether polyol, polyester polyol, polycarbonatepolyol, polycaprolactone polyol, an aliphatic hydrocarbon containing twoor more hydroxyl groups in the molecule, alicyclic hydrocarboncontaining two or more hydroxyl groups in the molecule, unsaturatedhydrocarbon containing two or more hydroxyl groups in the molecule, andthe like. The polyols can be used either independently or incombinations of two or more.

The above polyether polyol includes aliphatic polyether polyols,alicyclic polyether polyols and aromatic polyether polyols.

Examples of aliphatic polyether polyols include polyhydric alcohols suchas polyethylene glycol, polypropylene glycol, polytetramethylene glycol,polyhexamethylene glycol, polyheptamethylene glycol, polydecamethyleneglycol, pentaerythritol, dipentaerythritol, trimethylolpropane, alkyleneoxide addition polyols such as ethylene oxide addition triol oftrimethylolpropane, propylene oxide addition triol oftrimethylolpropane, ethylene oxide and propylene oxide addition triol oftrimethylolpropane, ethylene oxide addition tetraol of pentaerythritol,ethylene oxide addition hexaol of dipentaerythritol, polyether polyolsproduced by ring-opening polymerization of two or more ionicpolymerizable cyclic compounds, and the like.

Examples of the ionic polymerizable cyclic compounds include cyclicethers such as ethylene oxide, propylene oxide, butene-1-oxide,isobutene oxide, 3,3-bischloromethyl oxetane, tetrahydrofuran,2-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexeneoxide, styrene oxide, epichlorohydrin, glycidyl ether, allyl glycidylether, allyl glycidyl carbonate, butadiene monoxide, isoprene monoxide,vinyloxetane, vinyltetrahydrofuran, vinylcyclohexene oxide, phenylglycidyl ether, butyl glycidyl ether, and glycidyl benzoate. Examples ofspecific combinations of two or more of the above ionic polymerizablecyclic compounds include combinations of tetrahydrofuran and ethyleneoxide, tetrahydrofuran and propylene oxide, tetrahydrofuran and2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran,ethylene oxide and propylene oxide, butene-1-oxide and ethylene oxide,and tetrahydrofuran, butene-1-oxide, and ethylene oxide.

A polyether polyol produced by ring-opening polymerization of one of theabove ionic polymerizable cyclic compounds and cyclic imines such asethyleneimine, cyclic lactic acids such as β-propyolactone and glycolicacid, or dimethylcyclopolysiloxane can also be used.

Examples of the alicyclic polyether polyols include alkylene oxideaddition diol of hydrogenated bisphenol A, alkylene oxide addition diolof hydrogenated bisphenol F, and alkylene oxide addition diol of1,4-cyclohexanediol.

Examples of the aromatic polyether polyols include alkylene oxideaddition diol of bisphenol A, alkylene oxide addition diol of bisphenolF, alkylene oxide addition diol of hydroquinone, alkylene oxide additiondiol of naphthohydroquinone, and alkylene oxide addition diol ofanthrahydroquinone.

Polyether polyols are commercially available under the following tradenames: examples of aliphatic polyether polyols include PTMG650,PTMG1000, PTMG2000 (manufactured by Mitsubishi Chemical Corp.), PPG1000,EXCENOL1020, EXCENOL2020, EXCENOL3020, EXCENOL4020 (manufactured byAsahi Glass Co., Ltd.), PEG1000, Unisafe DC1100, Unisafe DC1800, UnisafeDCB1100, Unisafe DCB1800 (manufactured by Nippon Oil and Fats Co.,Ltd.), PPTG1000, PPTG2000, PPTG4000, PTG400, PTG650, PTG2000, PTG3000,PTGL1000, PTGL2000 (manufactured by Hodogaya Chemical Co., Ltd.),Z-3001-4, Z-3001-5, PBG2000, PBG2000B (manufactured by Daiichi KogyoSeiyaku Co., Ltd.), TMP30, PNT4 Glycol, EDA P4, EDA P8 (manufactured byNippon Nyukazai Co., Ltd.), and Quadrol (manufactured by Asahi DenkaKogyo K.K.); and examples of aromatic polyether polyols include UniolDA400, DA700, DA1000, and DB400 (manufactured by Nippon Oil and FatsCo., Ltd.).

The polyester polyol can be obtained by reacting a polyhydric alcoholwith a polybasic acid. Examples of a polyhydric alcohol include ethyleneglycol, polyethylene glycol, propylene glycol, polypropylene glycol,tetramethylene glycol, polytetramethylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexane dimethanol,1,2-bis(hydroxyethyl)cyclohexane, 2,2-diethyl-1,3-propanediol,3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol,glycerol, trimethylolpropane, ethylene oxide addition compound oftrimethylolpropane, propylene oxide addition compound oftrimethylolpropane, ethylene oxide and propylene oxide addition compoundof trimethylolpropane, sorbitol, pentaerythritol, dipentaerythritol, andalkylene oxide addition polyols. Examples of polybasic acids includephthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaricacid, adipic acid, sebacic acid, and the like. Commercially availableproducts of these polyester polyols, such as Kurapol P1010, KurapolP2010, PMIPA, PKA-A, PKA-A2, PNA-2000 (manufactured by Kuraray Co.,Ltd.), and the like can be used.

Moreover, examples of the polycarbonate polyols are polycarbonate diolsshown by the formula:

wherein R¹ represents an alkylene group having 2-20 carbon atoms, aresidual group of (poly)ethylene glycol, a residual group of(polypropylene glycol, or a residual group of (poly)tetramethyleneglycol, and m is an integer from 1 to 30.

Specific examples of R¹ are a residual group excluding both terminalhydroxyl groups from 1,4-butanediol, 1,5-pentanediol, neopentyl glycol,1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol, tetrapropylene glycol, and the like.

Polycarbonate polyols are commercially available under the trade names,for example, DN-980, DN-981, DN-982, DN-983 (manufactured by NipponPolyurethane Industry Co., Ltd.), PC-8000 (manufactured by PPG),PNOC1000, PNOC2000, PMC100, PMC2000 (manufactured by Kuraray Co., Ltd.),PLACCEL CD-205, CD-208, CD-210, CD-220, CD-205PL, CD-208PL, CD-210PL,CD-220PL, CD-205HL, CD-208HL, CD-210HL, CD-220HL, CD-210T, CD-221T(manufactured by Daicel Chemical Industries, Ltd.), and the like.

Examples of polycaprolactone polyols include polycaprolactone diolsobtained by the addition reaction of ε-caprolactone to a diol such asethylene glycol, polyethylene glycol, propylene glycol, polypropyleneglycol, tetramethylene glycol, polytetramethylene glycol,1,2-polybutylene glycol, 1,6-hexanediol, neopentyl glycol,1,4-cyclohexanedimethanol, and 1,4-butanediol. Polycaprolactone polyolsare commercially available under the trade names, for example, PLACCEL205, 205AL, 212, 212AL, 220, 220AL (manufactured by Daicel ChemicalIndustries, Ltd.) and the like.

Examples of aliphatic hydrocarbons containing two or more hydroxylgroups in the molecule include ethylene glycol, propylene glycol,tetramethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol,2,2-diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol,2-methyl-1,8-octanediol, hydrogenated polybutadiene with terminalhydroxyl groups, glycerol, trimethylolpropane, pentaerythritol, andsorbitol.

Examples of alicyclic hydrocarbons having two or more hydroxyl groups inthe molecule include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,1,2-bis(hydroxyethyl)cyclohexane, dimethylol compounds ofdicyclopentadiene, and tricyclodecanedimethanol.

Examples of unsaturated hydrocarbons containing two or more hydroxylgroups in the molecule include, a polybutadiene with terminal hydroxylgroups, a polyisoprene with terminal hydroxyl groups, and the like.

Furthermore, examples of polyols other than the above-mentioned polyolcompounds include β-methyl-δ-valerolactone diol, castor oil-modifieddiol, a polydimethylsiloxane with diols at the terminals, and apolydimethylsiloxane carbitol-modified diol.

The number average molecular weight of the polyols is preferably from 50to 15000, and more preferably from 100 to 8000.

The polyisocyanate is preferably a diisocyanate. Examples ofdiisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate,1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylenediisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate,4,4′-diphenylmethane diisocyanate, 3,3′-dimethylphenylene diisocyanate,4,4′-biphenylene diisocyanate, 1,6-hexane diisocyanate, isophoronediisocyanate, 2,2,4-trimethylhexamethylene diisocyanate,bis(2-isocyanate ethyl) fumarate, 6-isopropyl-1,3-phenyl diisocyanate,4-diphenylpropane diisocyanate, lysine diisocyanate, hydrogenateddiphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, andtetramethylxylylene diisocyanate. Among these, 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, hydrogenated xylylenediisocyanate, isophorone diisocyanate, hydrogenated diphenylmethanediisocyanate, and the like are preferable. These diisocyanate compoundsmay be used either singly or in combinations of two or more.

The hydroxyl group-containing (meth)acrylate compound is a(meth)acrylate compound in which the ester group includes a hydroxylsubstituent. Examples of such a compound are2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate,4-hydroxybutyl(meth)acrylate, 2-hydroxy-3-phenyloxypropyl(meth)acrylate,1,4-butanediol mono(meth)acrylate, 2-hydroxyalkyl(meth)acryloylphosphate, 4-hydroxy-cyclohexyl(meth)acrylate, 1,6-hexanediolmono(meth)acrylate, neopentyl glycol mono(meth)acrylate,trimethylolpropane di(meth)acrylate, trimethylolethane di(meth)acrylate,pentaerythritol tri(meth)acrylate, dipentaerythritolpenta(meth)acrylate. Additional examples of such hydroxylgroup-containing (meth)acrylates are compounds represented by thefollowing structural formula (2):

wherein R² represents a hydrogen atom or a methyl group and n denotes aninteger from 1 to 15, and preferably from 1 to 4.

Compounds obtained by the addition reaction of a (meth)acrylic acid anda compound containing a glycidyl group such as alkyl glycidyl ether,allyl glycidyl ether, and glycidyl (meth)acrylate can also be given asexamples of the (meth)acrylate compound. Among these compounds,2-hydroxyalkylacrylates such as for example2-hydroxyethyl(meth)acrylate, and 2-hydroxypropylacrylate are preferred.2-hydroxyethylacrylate is most preferred.

There are no specific limitations to the process for synthesizing theurethane (meth)acrylate (A). For instance, synthesis of the urethane(meth)acrylate (A) can be carried out according to the followingprocesses (i) to (iii):

(i) A process for reacting the polyisocyanate compound (b) with thehydroxyl group-containing (meth)acrylate compound (c), and reacting theresulting product with the polyol compound (a);

(ii) a process for reacting the polyol compound (a), the polyisocyanatecompound (b), and the hydroxyl group-containing (meth)acrylate compound(c) altogether; and

(iii) a process for reacting the polyol compound (a) with thepolyisocyanate compound (b), and reacting the resulting product with thehydroxyl group-containing (meth)acrylate compound.

In the synthesis of the urethane (meth)acrylate (A) used in the presentinvention, it is preferable to use a urethanization catalyst such ascopper naphthanate, cobalt naphthanate, zinc naphthanate, di-n-butyltindilaurate, triethylamine, 1,4-diazabicyclo[2.2.2]octane, and1,4-diaza-2-methylbicyclo[2.2.2]octane. The catalyst can be used in anamount of from 0.01 to 1 part by weight for 100 parts by weight of thetotal reaction components. The reaction is generally performed at atemperature of 0 to 90° C., and preferably 10 to 80° C.

The number average molecular weight of the urethane (meth)acrylate usedin the present invention is preferably from 400 to 20000, and morepreferably from 600 to 10000.

To ensure superior adhesion to substrates and adequate viscosity, theurethane (meth)acrylate (A) is incorporated in the composition of thepresent invention in an amount preferably from 5 to 85 parts by weight,more preferably from 15 to 65 parts by weight, and most preferably from15 to 55 parts by weight, for 100 parts by weight of the total amount ofthe components (A), (B), (C), (D) and (E).

The component (B) used in the present invention is ahydroxy(meth)acrylate in which there are at least 3 carbon atoms betweenthe hydroxyl group and the acrylate residue. Preferably, component (B)is an hydroxyalkyl(meth)acrylate in which the hydroxy group is presenton the γ, δ or ε position with respect to the acrylate; the δ positionis most preferred. Suitable compounds include 3-hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, 4-hydroxycyclohexyl(meth)acrylate, 1,6-hexanediol mono(meth) acrylate, neopentyl glycolmono(meth)acrylate, trimethylohpropane di(meth) acrylate,trimethylolethane di(meth) acrylate, pentaerythritol tri(meth) acrylate,dipentaerythritol penta(meth)acrylate. Additional examples of(meth)acrylates suitable for use in the present invention are compoundsrepresented by the following structural formula (2):

wherein R² represents a hydrogen atom or a methyl group and n denotes aninteger from 1 to 15, and preferably from 1 to 4, and by the followingstructural formula 2 (a):

wherein R² represents a hydrogen atom or a methyl group, and

X is a C₂-C₂₄ alkenyl,

a C₂-C₂₄ alkynyl,

an alkyl carbonate,

an alkyl urethane,

an alkyl urea,

an alkyl amido, or

an alkyl ether.

It will be appreciated by those skilled in the art that the selection ofX is such that the hydroxyl group and the acrylate residue are spacedapart by at least 3 carbon atoms. While the hydroxyl group in Formula 2,and in Formula 2(a) above, is shown in the terminal position of themolecule, it need not be. The hydroxyl group may be in any position inthe X linking group provided the hydroxyl group is separated from the(meth)acrylate moiety by 3 or more carbon atoms.

Compound B may also be a hydroxyarylacrylate wherein the aryl group maybe unsubstituted or substituted. In keeping with the invention, thehydroxyl group may be on the aromatic ring, or it may be on asubstituent of a substituted aromatic ring. The hydroxyl group ispreferably spaced apart from the (meth)acrylate group by 3 or morecarbon atoms.

Preferably, the molecular weight of the compound (B) molecule is 300 orless, more preferably less than 200. Of the above compounds,4-hydroxybutyl (meth)acrylate is particularly preferred, and iscommercially available from Osaka Organic Chemical Industry Co., Ltd, orfrom Mitsubishi.

The hydroxy(meth)acrylate, component (B), is preferably included in thecomposition of the present invention in an amount from 0.5 to 90 partsby weight, more preferably from 5 to 50 parts by weight and mostpreferably from 10 to 30 parts by weight, for 100 parts by weight of thetotal amount of the components (A), (B), (C), (D) and (E).

Compounds categorized under D or E can have hydroxyl groups as well. Itis preferred to obtain an optimal adhesion to polycarbonate, inparticular a good wet adhesion with compositions that before cure have aviscosity of about 1000 mpa.s or less, that a compound (B) is present,and that the amount of free hydroxyl groups in the composition is 0.3meq/g or more, preferably, 0.5 meq/g or more, and in particular 0.8meq/g or more. Generally, suitable adhesion is obtained with 4 meq/g orless, preferably with 3 meq/g or less.

The photo-polymerization initiator used as component (C) is preferablyat least one of 2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenyl-propan-1-one, and 1-hydroxy-cyclohexylphenyl ketone. Of these, 2,2-dimethoxy-1,2-diphenylethan-1-one and2-hydroxy-2-methyl-1-phenyl-propan-1-one are particularly preferred. Toensure excellent wet heat resistance and curability of the composition,the component (C) is used in an amount preferably from 0.1 to 20 partsby weight, more preferably from 0.5 to 15 parts by weight, and even morepreferably from 1 to 10 parts by weight, for 100 parts by weight of thetotal amount of the components (A), (B), (C), (D) and (E).

Commercially available products which can be used as thephoto-polymerization initiator for the component (C), include IRGACURE184, IRGACURE 500, IRGACURE 651, DAROCUR 1173, DAROCUR 4265(manufactured by Ciba Specialty Chemicals Co., Ltd.), and the like.

A photo-polymerization initiator other than the preferred initiatorsdescribed above may be used in the composition of the present inventionas a component (C) alone or in combination. Examples of otherphoto-polymerization initiators are 3-methylacetophenone,2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde,fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, benzophenone, 4-chlorobenzophenone,4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, benzoin ethylether, benzoin propyl ether, Michler's ketone, benzyl methyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one,4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl) ketone,2-methyl-i-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,2,4,6-trimethylbenzoylphenyl phosphinate,2,4,6-trimethylbenzoyldiphenylphosphine oxide,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,methylbenzoyl formate, thioxanethone, diethylthioxanthone,2-isopropylthioxanthone, 2-chlorothioxanthone, andoligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone].

These photo-polymerization initiators are commercially available underthe trade names, for example, IRGACURE 261, 369, 907, CGI-403, 819,1700, 1800, 1850 (manufactured by Ciba Specialty Chemicals Co., Ltd.),Lucirin TPO, LR8728, LR8893 (manufactured by BASF), Darocur 953, 1116,1664, 2273, 2959, ZL1 3331 (manufactured by Ciba Specialty ChemicalsCo., Ltd.), Ubecryl P36 (manufactured by UCB Co.), VICURE55(manufactured by Akzo), ESACURE KIP100F, KIP150 (manufactured byLamberti), and KAYACURE ITX, QTX, DETX, BMS (manufactured by NipponKayaku Co., Ltd.). The second group of photoinitiators can be added tothe first group to improve surface curability and increase the curingrate of the composition. A preferable combined use of the second groupof photoinitiators is to replace up to 70% of the initiator from thefirst group.

In addition to the above-described components (A), (B), and (C), a(meth)acrylate compound containing at least one (meth)acryloyl group inthe molecule, excluding the compounds used as the component (B), can beadded to the composition of the present invention as a component (D).Either a monofunctional compound having one (meth)acryloyl group or apolyfunctional compound having two or more (meth)acryloyl groups, or inappropriately proportioned combinations can be used as the component(D).

Examples of monofunctional monomers in the composition as component Dinclude methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl(meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl(meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl(meth)acrylate, octyl (meth)acrylate, iso-octyl (meth)acrylate,2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate,isodecyl (meth)acrylate, undecyl (meth) acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, stearyl(meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxyethyl(meth)acrylate, ethoxydiethylene glycol (meth)acrylate, benzyl(meth)acrylate, cyclohexyl (meth)acrylate, phenoxyethyl (meth)acrylate,polyethylene glycol mono(meth)acrylate, po lypropylene glycol mono(meth)acrylate, methoxyethylene glycol mono(meth)acrylate, ethoxyethyl(meth)acrylate, ethoxyethoxyethyl (meth)oacrylate, methoxypolyethyleneglycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate,dicyclopentadienyl (meth)acrylate, dicyclopentanyl (meth)acrylate,dicyclopentenyl (meth)acrylate, tricyclodecanyl (meth)acrylate, bornyl(meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate,dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate,7-amino-3,7-dimethyloctyl (meth)acrylate, (meth)acryloylmorpholine,2-(meth)acryloyloxyethylphthalic acid,2-(meth)acryloyloxyethylhexahydrophthalic acid,2-(meth)acryloyloxypropylphthalic acid,2-(meth)acryloyloxypropyltetrahydrophthalic acid,2-(meth)acryloyloxypropylhexahydrophthalic acid,2-(meth)acryloyloxyethylsuccinic acid, trifluoroethyl (meth)acrylate,tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate,octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate,mono[2-(meth)acryloyloxyethyl]phosphate,mono[2-(meth)acryloyloxyethyl]diphenylphosphate,mono[2-(meth)acryloyloxypropyl]phosphate, and compounds represented bythe following formulas (3) to (5):

wherein R² represents a hydrogen atom or a methyl group, R³ representsan alkylene group or a hydroxyalkylene group having 2-6 carbon atoms, R⁴represents a hydrogen atom or an alkyl group having 1-12 carbon atoms,and ?? denotes an integer from 0 to 20, preferably 1-8.

wherein R² represents a hydrogen atom or a methyl group, R⁵ representsan alkylene group having 2-8 carbon atoms, and r denotes an integer from0 to 8, preferably 1-8 and more preferably 1-4; and

wherein R² represents a hydrogen atom or a methyl group, R⁵ representsan alkylene group having 2-8 carbon atoms, s denotes an integer from 0to 8, and R⁶ represent a hydrogen atom or an alkyl group having 1-6carbon atoms.

These compounds are commercially available under the trade names, forexample, Aronix M101, M102, M110, M111, M113, M114, M117, M120, M152,M154, M5300, M5400, M5500, M5600 (manufactured by Toagosei Co., Ltd.),KAYARAD TC-110S, R-128H, R629, R644 (manufactured by Nippon Kayaku Co.,Ltd.), IPAA, AIB, SBAA, TBA, IAAA, HEXA, CHA, NOAA, IOAA, INAA, LA, TDA,MSAA, CAA, HDAA, LTA, STA, ISAA-1, ODAA, NDAA, IBXA, ADAA, TCDA, 2-MTA,DMA, Viscoat #150, #150D, #155, #158, #160, #190, #190D, #192, #193,#220, #320, #2311HP, #2000, #2100, #2150, #2180, MTG (manufactured byOsaka Organic Chemical Industry Co., Ltd.), NK Ester M-20G, M-40G,M-90G, M-230G, CB-1, SA, S, AMP-10G, AMP-20G, AMP-60G, AMP-90G, A-SA,NLA (manufactured by Shin-Nakamura Chemical Co., Ltd.), ACMO(manufactured by Kojin Co., Ltd.), Light acrylate IA-A, L-A, S-A, BO-A,EC-A, MTG-A, DPM-A, PO-A, P-200A, THF-A, IB-XA, HOA-MS, HOA-MPL,HOA-MPE, HOA-HH, IO-A, BZ-A, NP-EA, NP-10EA, HOB-A, FA-108, Epoxy EsterM-600A, Light Ester P-M (manufactured by Kyoeisha Chemical Co., Ltd.),FA-511, FA-512A, FA-513A (manufactured by Hitachi Chemical Co., Ltd.),AR-100, MR-100, MR-200, MR-260 (manufactured by Daihachi Chemical Co.,Ltd.), and JAMP-100, JAMP-514, JPA-514 (manufactured by Johoku ChemicalCo., Ltd.).

Examples of a polyfunctional compound that may be included in thecomposition as component D include ethylene glycol di(meth)acrylate,propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, polypropylene glycol di(meth)acrylate,neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,trimethylolpropane trioxyethyl(meth)acrylate, trimethylolpropanepolyoxyethyl(meth)acrylate, trimethylolpropanetrioxypropyl(meth)acrylate, trimethylolpropanepolyoxyethyl(meth)acrylate, tris(2-hydroxyethyl)isocyanuratedi(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,ethylene oxide addition bisphenol A di(meth)acrylate, ethylene oxideaddition bisphenol F di(meth)acrylate, propylene oxide additionbisphenol A di(meth)acrylate, propylene oxide addition bisphenol Fdi(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, bisphenol Adiepoxydi(meth)acrylate, bisphenol F diepoxydi(meth)acrylate,bis[2-(meth)acryloyloxyethyl]phosphate,bis[2-(meth)acryloyloxypropyl]phosphate, andtris[2-(meth)acryloyloxyethyl]phosphate.

Examples of commercially available products of the polyfunctionalcompounds that may be included in the composition as component D includeSA-1002, SA-2006, SA-2007, SA-4100, SA-5001, SA-6000, SA-7600, SA-8000,SA-9000 (manufactured by Mitsubishi Chemical Corp.), Viscoat #195,#195D, #214HP, #215, #215D, #230, #230D, #260, #295, #295D, #300,#310HP, #310HG, #312, #335HP, #335D, #360, GPT, #400, V#540, #700, GPT(manufactured by Osaka Organic Chemical Industry Co., Ltd.), KAYARADMANDA, R-526, NPGDA, PEG400DA, R-167, HX-220, HX-620, R-551, R-712,R-604, R-684, GPO-303, TMPTA, THE-330, TPA-320, TPA-330, PET-30,RP-1040, T-1420, DPHA, D-310, D-330, DPCA-20, DPCA-30, DPCA-60, DPCA-120(manufactured by Nippon Kayaku Co., Ltd.), Aronix M210, M208, M215,M220, M225, M233, M240, M245, M260, M270, M305, M309, M310, M315, M-320,M-350, M-360, M-400, M-408, M-450 (manufactured by Toagosei Co., Ltd.),SR-212, SR-213, SR-355 (manufactured by Sartomer Co., Ltd.), SP-1506,SP-1507, SP-1509, SP-1519-1, SP-1563, SP-2500, VR60, VR77, VR90(manufactured by Showa Highpolymer Co., Ltd.), Light Ester P-2M(manufactured by Kyoeisha Chemical Co., Ltd.), Viscoat 3PA (manufacturedby Osaka Organic Chemical Industry Co., Ltd.), and EB-169, EB-179,EB-3603, R-DX63182 (manufactured by Daicel UCB Co., Ltd.). The component(D) is used to provide the composition with a desired range ofviscosity, Tg, refractive index, and the like. The component (D) ispreferably used in an amount of 0-70% by weight, more preferably 5-60%by weight and most preferably 20 to 50% by weight for the total weightof the components A, B, C, D and E.

In addition to the above components (A), (B), and (C), radicallypolymerizable compounds other than compounds containing an acrylategroup may be incorporated in the composition of the present invention ascomponent (E). Examples of such compounds include N-vinylpyrrolidone,N-vinylcaprolactam, vinyl acetate, vinyl propionate, styrene,alkylacrylamides, divinylbenzene, and unsaturated polyesters. However,N-vinyl-pyrrolidone preferably is not used. The unsaturated polyesterpreferably is an ester of a dicarboxylic acid containing a radicallypolymerizable unsaturated double bond and an alcohol. Examples of adicarboxylic acid containing a radically polymerizable unsaturateddouble bond include maleic acid, maleic anhydride, itaconic acid, andfumaric acid. Examples of an alcohol include monohydric alcohols such asmethanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-hexanol,cyclohexanol, and 2-ethylhexyl alcohol; (poly)ethylene glycols such asethylene glycol, diethylene glycol, triethylene glycol, and the like;(poly)propylene glycols such as propylene glycol, dipropylene glycol,and tripropylene glycol; dihydric alcohols such as 1,6-hexanediol; andtrihydric alcohols such as glycerol and trimethylolpropane.

Furthermore, an epoxy resin, polyamide, polyamideimide, polyurethane,polybutadiene, chloroprene, polyether, polyester, pentadienederivatives, SBS (styrene/butadiene/styrene block copolymer),hydrogenated products of SBS, SIS (styrene/isoprene/styrene blockcopolymer), petroleum resin, xylene resin, ketone resin, fluorine-basedoligomer, silicone-based oligomer, polysulfide-based oligomer, and thelike may be incorporated in the composition of the present invention asother additives.

The component (E), as noted above, need not be included in thecomposition of the present invention. However, when component (E) isincluded, it is generally included in the uncured composition in anamount of less than 60 parts by weight, and desirably from about 1 to 30parts by weight of the total weight of the components (A), (B), (C), (D)and (E).

The composition of the present invention may further include variouspaint additives other than the above additives, for example,antioxidants, UV absorbers, light stabilizers, aging preventives, silanecoupling agents, antifoaming agents, leveling agents, antistatic agents,surfactants, preservatives, heat polymerization inhibitors,plasticizers, and wettability improvers. Examples of antioxidantsinclude Irganox 245, 259, 565, 1010, 1035, 1076, 1081, 1098, 1222, 1330(manufactured by Ciba Specialty Chemicals Co., Ltd.), and the like.

Examples of UV absorbers include benzotriazole type and triazine type UVabsorbers and commercially available products such as Tinuvin P, 234,320, 326, 327, 328, 213, 400 (manufactured by Ciba Specialty ChemicalsCo., Ltd.), Sumisorb 110, 130, 140, 220, 250, 300, 320, 340, 350, 400(manufactured by Sumitomo Chemical Industries Co., Ltd.), and the like.

Examples of light stabilizers include commercially available productssuch as Tinuvin 144, 292, 622LD (manufactured by Ciba SpecialtyChemicals Co., Ltd.), Sanol LS440, LS770 (manufactured by Sankyo Co.,Ltd.), and Sumisorb TM-061 (manufactured by Sumitomo Chemical IndustriesCo., Ltd.). Light stabilizers are added in the amount of 5 parts byweight or less of 100 parts by weight of the composition of the presentinvention.

Examples of aging preventives include phenol type, allylamine type, andketone amine type aging preventives. Examples of commercially availableproducts of these aging preventives include Antigene W, S, P, 3C, 6C,RD-G, FR, and AW (manufactured by Sumitomo Chemical Industries Co.,Ltd.).

A preferred additive is a silane coupling agent.

Examples of silane coupling agents include:γ-mercaptopropylmethylmonomethoxysilane,γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane,γ-mercaptopropylmonoethoxys ilane, γ-mercaptopropyldiethoxysilane,γ-mercaptopropyltriethoxysilane, β-mercaptoethylmonoethoxysilane,β-mercaptoethyltriethoxysilane, β-mercaptoethyltriethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, γ-glycidoxylpropyltrimethoxysi lane,γ-glycidoxyl propylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane,γ-chloropropyltrimethoxysilane, andγ-methacryloyloxypropyltrimethoxysilane. Examples of commerciallyavailable products of these compounds include SILAACE S310, S311, S320,S321, S330, S510, S520, S530, S610, S620, S710, S810 (manufactured byChisso Corp.), SH6062, AY43-062, SH6020, SZ6023, SZ6030, SH6040, SH6076,SZ6083 (manufactured by Toray-Dow Corning Silicone Co., Ltd.), KBM403,KBM503, KBM602, KBM603, KBM803, KBE903 (manufactured by Shin-EtsuSilicone Co., Ltd.), and the like. The silane coupling agent ispreferably included in the uncured adhesive in an amount of from 0.2 to5 wt % based on the total weight of compounds (A), (B), (C), (D) and (E)in the uncured adhesive.

Examples of antifoaming agents include organic copolymers excludingsilicon and fluorine which are commercially available under the tradenames, for example, Fluorene AC-202, AC-300, AC-303, AC-326F, AC-900,AC-1190, and AC-2000 (manufactured by Kyoeisha Yushi Co., Ltd.);silicon-containing antifoaming agents which are commercially availableunder the trade names, for example, Fluorene AC-901, AC-950, AC-1140,AO-3, AO-4OH (manufactured by Kyoeisha Yushi Co., Ltd.), FS1265, SH200,SH5500, SC5540, SC5570, F-1, and SD5590 (manufactured by Toray-DowCorning Silicone Co., Ltd.); fluorine-containing antifoaming agentswhich are commercially available under the trade names, for example,MEGAFAC F-142D, F-144D, F-178K, F-179, F-815 (manufactured by DainipponInk and Chemicals, Inc.); and the like.

Examples of leveling agents include Polyflow No. 7, No. 38, No. 50E, S,75, No. 75, No. 77, No. 90, No. 95, No. 300, No. 460, ATF, KL-245(manufactured by Kyoeisha Yushi Co., Ltd.), and the like.

The amount of these additives can be appropriately determined so thatthe object of the present invention is not adversely affected.

The viscosity of the composition of the present invention is preferablyfrom 10 to 10000 mPa·s, more preferably from 50 to 5000 mPa·s, and evenmore preferably from 100 to 2000 mPa·s.

These components are incorporated so that the glass transitiontemperature of the resulting cured product is usually from −50 to 200°C., preferably from −30 to 200° C., and more preferably from 0 to 120°C. If the glass transition temperature is too low, the cured productsmay soften when heated in summer or in a closed and sunny room, therebyresulting in the decreased adhesion strength. This may cause the adheredmembers to peel off or slip out. On the contrary, if the glasstransition temperature is too high, adhesion may be insufficient or thecoated members break when dropped or bent.

The glass transition temperature described here is defined as thetemperature at which a loss tangent (tan d) reaches a peak when measuredby a dynamic viscoelasticity measuring device at an oscillationfrequency of 10 Hz.

The composition of the present invention can be cured by exposure toultraviolet radiation, visible rays, electron beams, and the like in thesame manner as in the case of using conventional photocurable resincompositions. The composition of the present invention can be easilycured by filling the composition between the members to be coated sothat the thickness of the adhesive layer is from 10 to 100 μm andirradiating the adhesive layer at a dose of 50 to 2000 mJ/cm² using ametal halide lamp, whereby the members can be glued to each other.

Further, the cured products made from the composition of the presentinvention are desired to have excellent transparency. For example, it ispreferable that the cured products with a thickness of 60 μm have alight transmittance of 90% or more at a wave length of 600 to 700 nm. Ifthe light transmittance is less than 90%, not only is the appearance ofthe optical disks impaired, but also the light for reading theinformation recorded on the disk is reduced by the adhesive layer,thereby making it difficult to read the information. Therefore, inpreparing the composition of the present invention, each componentshould be blended so that the light transmittance of the resulting curedproduct satisfy this requirement.

In addition, it is desirable to blend each component so that therefractive index of the photocured product made from the composition ofthe present invention is in the range from 1.4 to 1.7, and preferablyfrom 1.51 to 1.70 at 25° C. If the refractive index is out of thisrange, reading of the information recorded on the disk may be difficult.

The composition of the present invention exhibits excellent adhesion toplastics such as polycarbonate (PC) and methyl polymethacrylate (PMMA),metals such as gold and aluminum, and inorganic materials such as glass.Therefore, the composition of the present invention is suitable as anadhesive for optical disks.

EXAMPLES

The present invention will be explained in more detail by way ofexamples, which are not intended to be limiting of the presentinvention.

Synthesis of Urethane Acrylate as Component (A) Synthesis Example 1

209 g of isophorone diisocyanate, 0.2 g of3,5-di-t-butyl-4-hydroxytoluene, and 0.8 g of di-n-butyltin dilauratewere placed in a separable flask (1 liter) equipped with a stirrer and athermometer. The mixture was stirred and then cooled to 10° C. in a coldwater bath in dry air. 109 g of 2-hydroxyethyl acrylate was graduallyadded to the mixture and reacted for one hour while maintaining thetemperature at 10 to 35° C. Then, 480 g of polytetramethylene glycolhaving a hydroxyl value of 109.7 mg KOH/g (trade name: PTMG1000,manufactured by Mitsubishi Chemical Corp.) was added and the resultingmixture was stirred at 40 to 60° C. for 5 hours to react, thus obtainingurethane acrylate (Al) having a number average molecular weight of 1650.

Synthesis Example 2

Urethane acrylate (A2) having a number average molecular weight of 1530was prepared in the same manner as in Synthetic Example 1, except forusing 472 g of polyester diol having a hydroxyl value of 111.7 mg KOH/g(trade name: Kurapol P1010, manufactured by Kuraray Co., Ltd.) insteadof the polytetramethylene glycol used in Synthetic Example 1.

Synthesis Example 3

Urethane acrylate (A3) having a number average molecular weight of 2570was prepared in the same manner as in Synthetic Example 1, except forusing 956 g of polyether diol having a hydroxyl value of 55.2 mg KOH/g(trade name: PTG-L 2000, manufactured by Hodogaya Chemical Co., Ltd.)instead of the polytetramethylene glycol used in Synthesis Example 1.

Examples and Comparative Examples Preparation of Compositions forForming Radiation Curable Coating Films

The components shown in Table 1 were placed in a reaction vesselequipped with a stirrer and stirred to prepare the compositions ofExamples 1-3 and Comparative Examples 1-4. The components shown in Table1 are as follows. The amount of each component is indicated by parts byweight in Table 1.

Component (B)

B1: 4-Hydroxybutyl acrylate (4HBA, manufactured by Osaka OrganicChemical Industry Co., Ltd.)

B2: 4-hydroxycyclohexyl acrylate (4HCHA)

Component (C)

C1-1: 2,2-Dimethoxy-1,2-diphenylethan-1-on (Irgacure 651, manufacturedby Ciba Specialty Chemicals Co., Ltd.)

C1-2: 2-Hydroxy-2-methyl-1-phenyl-propan-1-on (Darocur 1173,manufactured by Ciba Specialty Chemicals Co., Ltd.)

C2-1: 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one(Irgacure 369, manufactured by Ciba Specialty Chemicals Co., Ltd.)

C2-2: 2-Methyl-1[4-(methylthio)phenyl-2-morpholino-propan-1-one(Irgacure 907, manufactured by Ciba Specialty Chemicals Co., Ltd.)

C2-3: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO,manufactured by BASF)

Component (D)

D1: Hydroxypivalic acid neopentyl glycol diacrylate (KAYARAD MANDA,manufactured by Nippon Kayaku Co., Ltd.)

D2: Phenoxyethyl acrylate (Viscoat 192, manufactured by Osaka OrganicChemical Industry Co., Ltd.)

D3: Lauryl acrylate (LA, manufactured by Osaka Organic Chemical IndustryCo., Ltd.)

D4: Isobornyl acrylate (IBXA, manufactured by Osaka Organic ChemicalIndustry Co., Ltd.)

D5: 2-Acryloyloxypropyl hydrogen phthalate (Viscoat 2100, manufacturedby Osaka Organic Chemical Industry Co., Ltd.)

D6: Nonylphenol EO-modified acrylate (M111, manufactured by ToagoseiCo., Ltd.)

D7: Ethoxylated trimethylolpropane triacrylate (A-TMPT-3EO, manufacturedby Shin-Nakamura Chemical Co., Ltd.)

Adhesion to substrates and wet heat resistance of the compositionsprepared above (Examples 1-3 and Comparative Examples 1-4) were measuredaccording to the following methods.

(1) Adhesion to Substrates

Adhesion to a Polycarbonate Substrate:

The composition was applied on a PC substrate (Panlite, manufactured byTeijin Chemicals Ltd.) using a spin coater. The coating was irradiatedwith light at a dose of 100 mJ/cm2 in a nitrogen atmosphere to form acured coating with a thickness of 50 mm. The cured coating was thensubjected to the cross-cut cellophane tape peeling test. Specifically, 1cm notches crossing at the center of the cured coating at almost a rightangle were cut using a cutter knife. A cellophane tape was applied tothe cured coating and then rapidly peeled off. When the cured coatingpeeled off in the cellophane tape peeling test, the adhesion wasdetermined to be bad, which is indicated by “X” in Table 1. When thecured coating did not peel off, the adhesion was determined to be good,which is indicated by “O” in Table 1.

Adhesion to Aluminum:

The composition was applied on an aluminum coating formed by vapordeposition using a sputtering method on the same PC substrate as thatused in the above test using a spin coater. The coating was irradiatedwith light at a dose of 100 mJ/cm2 in a nitrogen atmosphere to form acured coating with a thickness of 50 mm. The cured coating was thensubjected to the cross-cut cellophane tape peeling test in the samemanner as in the case of the above PC substrate. When part or all of thealuminum coating peeled off from the PC substrate, the adhesion of thecured coating was determined to be good, which is indicated by “O” inTable 1. When the aluminum coating did not peel off at all, the adhesionwas determined to be bad, which is indicated by “X” as shown in Table 1.

Adhesion to Gold:

The composition was applied on a gold coating formed by vapor depositionusing a sputtering method on the same PC substrate as that used in theabove test using a spin coater. The coating was irradiated with light ata dose of 100 mJ/cm2 in a nitrogen atmosphere to form a cured coatingwith a thickness of 50 mm. The cured coating was then subjected to thecross-cut cellophane tape peeling test in the same manner as in the caseof the above PC substrate. When part or all of the gold coating peeledoff from the PC substrate, the adhesion was determined to be good, whichis indicated by “O” in Table 1. When the gold coating did not peel offat all, the adhesion was determined to be bad, which is indicated by “X”in Table 1.

(2) Wet Heat Resistance

A combination “1” of (a) a substrate formed by applying an aluminumcoating on the PC substrate by sputtering and (b) a PC substrate and acombination “2” of (a) a substrate formed by applying an aluminumcoating on the PC substrate by sputtering and (c) a substrate formed byapplying a gold coating on the PC substrate by sputtering were provided.The two substrates in each combination “1” or “2” were attached byproducing a coating with a thickness of about 50 mm using a spin coater.The combined substrates “1” and “2” were irradiated with light at a doseof 500 mJ/cm2 from the side of the PC substrate (b) or the substrateformed by applying a gold coating on a PC substrate (c), to adhere apair of substrates (a) and (b) or (a) and (c). The adhered substrateswere then allowed to stand at 800° C. and 95% relative humidity (RH) for96 hours in a thermo-hygrostat. When any abnormalities such as bubblesand corrosion were observed on the adhesive layer or in the interfacebetween the adhesive layer and the substrate, the wet heat resistancewas determined to be bad, which is indicated by “X” in Table 1. When nosuch abnormalities were observed, the wet heat resistance was determinedto be good, which is indicated by “O” in Table 1.

The composition of Example 1 comprising the components (A), (B), (C) and(D) exhibits superior adhesion properties including PC, Al, and Auadhesion and has excellent wet heat resistance. The composition ofExample 2, which does not contain the components (D) but a large amountof the component (B), exhibited especially excellent wet heatresistance. The composition of Example 3, the composition according toclaim 3 which does not include the component (C-2), showed satisfactoryresults in all evaluation items. On the other hand, the wet heatresistance was poor in the composition of Comparative Examples 1, 2 and3 which do not contain the component (B). Comparative Examples 2 showedinferior Al and Au adhesion.

TABLE 1 Comparative Example Example Component 1 2 3 1 2 3 A1 30 30 A2 5030 A3 30 30 B1 30 70 B2 20 C1-1  2  3 C1-2  4  2  2 C2-1  2 C2-2  2  2 2 C2-3  2  2 D1 15 35 D2 20 D3 20 35 D4 35 D5 15 D6 35 35 D7 35Adhesion to PC ◯ ◯ ◯ ◯ ◯ ◯ Adheston to Al ◯ ◯ ◯ ◯ X ◯ Adhesion to Au ◯ ◯◯ ◯ X ◯ Wet heat resistance ◯ ◯ ◯ X X X

Example 4

The components shown in Table 2 were placed in a reaction vesselequipped with a stirrer and stirred to prepare the composition.

TABLE 2 Composition Parts by wt. Oligomer⁽¹⁾ 33 VR 77⁽²⁾ 15 4-HB 30 4EGA⁽³⁾ 22 Irgacure 651 3 Darocure 1173 3 Kayacure EPA 0.5 Irganox 10350.3 SH 6062⁽⁴⁾ 1.0 ⁽¹⁾The idealized structure for the oligomer isH-I-PTGL 2000-I-H wherein H is hydroxyethylacrylate, I isisophoronediisocyanate, and PTGL 2000 is a copolymer of tertrahydrofuranand methyltetrahydrofuran (The oligomer is available from Hodogaya inJapan.) ⁽²⁾is bisphenol-A-epoxy acrylate. ⁽³⁾is tetraethyleneglycoldiacrylate. ⁽⁴⁾is γ-mercapto propyl trimethoxy silane.

The adhesives were applied on optical disks or in the wet heatresistance test described above. Excellent results are obtained with thecomposition described in Table 2.

The adhesive composition of the present invention not only cures fast,has a high light transmittance, exhibits superior adhesion to resins,reflecting films, translucent films, and the like for forming opticaldisks, but also possesses superior wet heat resistance. The adhesive isextremely useful for manufacturing optical disks as compared toconventional adhesives.

We claim:
 1. An adhesive for optical disks comprising components (A),(B), and (C), wherein: component A is a urethane acrylate ormethacrylate comprising a backbone, urethane groups and an acrylate or amethacrylate group, component B is an hydroxy acrylate or methacrylatewherein the hydroxyl group and said acrylate or methacrylate group areseparated by at least 3 carbons, component C comprises at least onephotoinitiator, said adhesive composition containing hydroxyl groups inan amount of at least 0.3 meq/g.
 2. The adhesive according to claim 1,wherein component (B) is a hydroxyalkyl acrylate or methacrylate whereinthe hydroxyl group is present on the γ, δ or ε position with respect tothe acrylate or methacrylate.
 3. The adhesive according to claim 1,wherein the component (B) is 4-hydroxybutyl acrylate or 4-hydroxybutylmethacrylate.
 4. The adhesive according to any one of claims 1-3,further comprising: a mono-functional or poly-functional acrylate or amono-functional or poly-functional methacrylate other than component (A)or component (B).
 5. The adhesive according to any one of claims 1-3further comprising: a radically polymerizable compound other thancompounds comprising acrylate or methacrylate groups.
 6. The adhesiveaccording to claim 4 further comprising: a radically polymerizablecompound other than compounds comprising acrylate or methacrylategroups.
 7. The adhesive according to any one of claims 1-3, whereincomponent (C) comprises at least one compound selected from the groupconsisting of 2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenyl-propan-1-one, and1-hydroxy-cyclokexylphenylketone.
 8. The adhesive according to claim 4,wherein component (C) comprises at least one compound selected from thegroup consisting of 2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenyl-propan-1-one, and1-hydroxy-cyclokexylphenylketone.
 9. The adhesive according to claim 5,wherein component (C) comprises at least one compound selected from thegroup consisting of 2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenyl-propan-1-one, and1-hydroxy-cyclokexylphenylketone.
 10. The adhesive according to claim 6,wherein component (C) comprises at least one compound selected from thegroup consisting of 2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenyl-propan-1-one, and1-hydroxy-cyclokexylphenylketone.
 11. The adhesive composition accordingto any one of claims 1-3, wherein the composition has a viscosity of100-2000 mPa's.
 12. The adhesive composition according to claim 4,wherein the composition has a viscosity of 100-2000 mPa's.
 13. Theadhesive composition according to claim 5, wherein the composition has aviscosity of 100-2000 mPa's.
 14. The adhesive composition according toclaim 6, wherein the composition has a viscosity of 100-2000 mPa's. 15.The adhesive composition according to claim 7, wherein the compositionhas a viscosity of 100-2000 mPa's.
 16. The adhesive compositionaccording to claim 8, wherein the composition has a viscosity of100-2000 mPa's.
 17. The adhesive composition according to claim 9,wherein the composition has a viscosity of 100-2000 mPa's.
 18. Theadhesive composition according to claim 10, wherein the composition hasa viscosity of 100-2000 nPa's.
 19. The adhesive composition according toany one of claims 1-3, wherein said adhesive composition containshydroxyl groups in an amount of from about 0.3 meq/g to 4 meq/g.
 20. Theadhesive according to claim 4, wherein said adhesive compositioncontains hydroxyl groups in an amount of from about 0.3 meq/g to 4meq/g.
 21. The adhesive according to claim 5, wherein said adhesivecomposition contains hydroxyl groups in an amount of from about 0.3meq/g to 4 meq/g.
 22. The adhesive according to claim 6, wherein saidadhesive composition contains hydroxyl groups in an amount of from about0.3 meq/g to 4 meq/g.
 23. The adhesive according to claim 7, whereinsaid adhesive composition contains hydroxyl groups in an amount of fromabout 0.3 meq/g to 4 meq/g.
 24. The adhesive according to claim 8,wherein said adhesive composition contains hydroxyl groups in an amountof from about 0.3 meq/g to 4 meq/g.
 25. The adhesive according to claim9, wherein said adhesive composition contains hydroxyl groups in anamount of from about 0.3 meq/g to 4 meq/g.
 26. The adhesive according toclaim 10, wherein said adhesive composition contains hydroxyl groups inan amount of from about 0.3 meq/g to 4 meq/g.
 27. An optical diskcomprising a first substrate, a second substrate and an adhesivetherebetween, for adhering said substrates, wherein said adhesive, inuncured form, is an adhesive according to any one of claims 1-3.
 28. Anoptical disk comprising a first substrate, a second substrate and anadhesive therebetween, for adhering said substrates, wherein saidadhesive, in uncured form, is an adhesive according to claim
 4. 29. Anoptical disk comprising a first substrate, a second substrate and anadhesive therebetween, for adhering said substrates, wherein saidadhesive, in uncured form, is an adhesive according to claim
 5. 30. Anoptical disk comprising a first substrate, a second substrate and anadhesive therebetween, for adhering said substrates, wherein saidadhesive, in uncured form, is an adhesive according to claim
 6. 31. Theoptical disk according to claim 27, wherein the cured product obtainedby irradiation of said adhesive with UV light has a glass transitiontemperature from 0 to 120° C.
 32. The optical disk according to claim28, wherein the cured product obtained by irradiation of said adhesivewith UV light has a glass transition temperature from 0 to 120° C. 33.The optical disk according to claim 29, wherein the cured productobtained by irradiation of said adhesive with UV light has a glasstransition temperature from 0 to 120° C.
 34. The optical disk accordingto claim 30, wherein the cured product obtained by irradiation of saidadhesive with UV light has a glass transition temperature from 0 to 120°C.
 35. The optical disk according to claim 27, wherein the cured productobtained by irradiation of said adhesive with UV light has a refractiveindex from 1.4 to 1.7.
 36. The optical disk according to claim 28,wherein the cured product obtained by irradiation of said adhesive withUV light has a refractive index from 1.4 to 1.7.
 37. The optical diskaccording to claim 29, wherein the cured product obtained by irradiationof said adhesive with UV light has a refractive index from 1.4 to 1.7.38. The optical disk according to claim 30, wherein the cured productobtained by irradiation of said adhesive with UV light has a refractiveindex from 1.4 to 1.7.
 39. An optical disk comprising a first substrate,a second substrate and an adhesive therebetween, for adhering saidsubstrates, wherein said adhesive, in uncured form is an adhesiveaccording to claim
 7. 40. An optical disk comprising a first substrate,a second substrate and an adhesive therebetween, for adhering saidsubstrates, wherein said adhesive, in uncured form is an adhesiveaccording to claim
 8. 41. An optical disk comprising a first substrate,a second substrate and an adhesive therebetween, for adhering saidsubstrates, wherein said adhesive, in uncured form is an adhesiveaccording to claim
 9. 42. An optical disk comprising a first substrate,a second substrate and an adhesive therebetween, for adhering saidsubstrates, wherein said adhesive, in uncured form is an adhesiveaccording to claim
 10. 43. An optical disk according to claim 42,wherein the cured product obtained by irradiation of said adhesive withUV light has a glass transition temperature from 0 to 120° C.
 44. Anoptical disk according to claim 42, wherein the cured product obtainedby irradiation of said adhesive with UV light has a refractive indexfrom 1.4 to 1.7.
 45. The optical disk according to claim 39, wherein thecured product obtained by irradiation of said adhesive with UV light hasa glass transition temperature from 0 to 120° C.
 46. The optical diskaccording to claim 40, wherein the cured product obtained by irradiationof said adhesive with UV light has a glass transition temperature from 0to 120° C.
 47. The optical disk according to claim 41, wherein the curedproduct obtained by irradiation of said adhesive with UV light has aglass transition temperature from 0 to 120° C.
 48. The optical diskaccording to claim 39, wherein the cured product obtained by irradiationof said adhesive with UV light has a refractive index from 1.4 to 1.7.49. The optical disk according to claim 40, wherein the cured productobtained by irradiation of said adhesive with UV light has a refractiveindex from 1.4 to 1.7.
 50. The optical disk according to claim 41,wherein the cured product obtained by irradiation of said adhesive withUV light has a refractive index from 1.4 to 1.7.